1. Field of the Invention
The present invention relates to an air chuck that can center a disk.
2. Background Information
Hard disk drives contain a plurality of recording heads that are located adjacent to one or more magnetic disks. The recording heads can write and read information on the magnetic disks by magnetizing or sensing the magnetic field of the disks, respectively. The storage of information is typically segmented into a plurality of circumferential tracks that extend across the surfaces of the disks. Each track typically contains a servo field. The servo field includes servo bits that are used by the drive to center a head onto the centerline of a track.
Disks are typically tested for manufacturing imperfections before being assembled into a drive. The disks are typically tested in an apparatus commonly referred to as a certifier. The disks are manually loaded onto a spindle motor of the certifier. The certifier has heads which are coupled to circuits that can write and then read signals from the disks. The signal read back from the disk is analyzed to identify any disk imperfections. Additionally, the mechanical surface of the disk can be inspected to identify asperities, etc.
After certification, servo information is then written onto the disk. The servo information is typically written by an apparatus commonly referred to as a servo writer. Like the certifier, a servo writer will have a spindle motor, heads and electronic circuitry.
It is desirable to write the servo information along tracks that are concentric with the center opening of the disk. Concentric tracks decrease the seek and centering time required to move the heads within a drive. Spindle motors of the prior art typically have mechanical, vacuum, or air driven clamps that clamp the disk(s) onto a centering post. Even with tight manufacturing tolerance requirements there is always a small space between the post and the disk. This space may allow the disk to be off-center from the centering post. The space will create non-concentric servotracks. Additionally, centrifugal forces caused by rotating off-center disks can produce structural vibrations which result in differential head to disk motions. The differential head to disk motions will create inaccuracies in the resultant servo information. It is therefore desirable to provide a chuck that can accurately center a disk onto a spindle motor.
One embodiment of the present invention is a chuck which has a plurality of cartridges that can exert essentially equal forces onto an inner edge of a disk. The equal forces center the disk onto a spindle motor. The spindle motor may be part of a servo writer for writing servo information onto the disk. Each cartridge may include a biasing element that can move within a variable orifice and engage the inner edge of the disk.